In one embodiment, carbon nanotubes (CNTs) have unique properties that make them potentially useful in many applications in optics, electronics, nanotechnology, and materials science. CNTs display unusual strength and exceptional electrical properties, and excellent heat conduction. A number of techniques have been developed to synthesize CNTs, these include: laser ablation, arc discharge, high pressure carbon monoxide (HiPCO), and chemical vapor deposition (CVD).
CVD growth can occur in vacuum or at atmospheric pressure. A metal nanoparticle may be used as a catalyst. Typical catalysts include nickel, iron, cobalt, or a combination. The catalysts can be patterned, annealed, or plasma etched. Growth of nanotubes is initiated by blending two gases in the CVD reactor. These gases include a process gas like ammonia, nitrogen, hydrogen and a carbon-containing gas like ethylene, ethanol, methane. CNTs grow at the metal catalysts.
There are two major challenges in the field of CNT's: a) a synthesis technique to produce CNTs with reproducible diameter and electronic properties, b) ability to place and align CNTs at desired positions in nanoelectronic circuits. The present invention addresses both challenges. In the nano or micro CVD process, described herein, the substrate is exposed to one or more precursors. The precursors react and/or decompose on the substrate surface. The reaction is directed by the localized heating provided by the heated tips. Eventually the desired deposit is created on the substrate. Nano CVD is a maskless process. A number of materials can be grown on the substrate without a mask. NanoCVD can be used to deposit materials in various forms, including: monocrystalline, polycrystalline, amorphous, and epitaxial. These materials include: various dielectrics, titanium nitride, SiO2, silicon-germanium, silicon, silicon oxynitride, silicon nitride, silicon carbide, localized oxidation, filaments, carbon nanotubes, carbon nanofibers, carbon fiber, tungsten, synthetic diamonds.